Immunoassays, such as chemiluminescent immunoassays, generally require two antibody preparations, a first antibody used to capture and immobilize a target antigen molecule, and a second antibody used to attach a detection label to the antigen.
Immobilization of the antigen to be detected in an immunoassay may be accomplished using magnetizable beads, and detection may be accomplished by using a suitable visualant such as isoluminol chemiluminescence. The assay involves the following major steps. For example, a sample containing the antigen is mixed with a first antibody to the antigen which is coupled to magnetizable latex beads, and the mixture is allowed to react. A second antibody, typically to a different epitope on the antigen, coupled to isoluminol, is added to the sample in step 1 and the mixture is allowed to react. A magnetic field is applied to retain the magnetizable beads (with antigen bound, labeled antibody) against the inside wall of the container. A wash fluid is introduced to remove the unbound labeled antibody. Washing the magnetizable beads typically occurs by immobilizing the beads in the magnetic field, introducing a wash fluid, removing the magnetic field, and repeatedly expelling beads into and aspirating the beads from a container to recover all of the beads and to homogeneously mix and resuspend the beads in the wash fluid. The magnetizable beads with antigen bound, labeled antibody are resuspended in a suitable optical cuvette. An activating reagent such as hydrogen peroxide which activates isoluminol is added with the beads in the cuvette and light is emitted in a chemiluminescent reaction. The light emitted from the chemiluminescent reaction is detected using a suitable photodetector. For some applications, additional steps of reagent addition and/or washing may be necessary.